Technical Field
The present disclosure relates to devices and methods for controlling electrical power during power failure.
Description of Related Art
Devices are available for delivering electrical power to a load when a main source of electrical power to the load is absent. For example, emergency lighting may be provided during a power outage by switching the lighting power source to a backup battery.
In an effort to provide switching capability to control battery utilization, power failure products may include a switching feature using variations of an impedance test on the line. The impedance test is designed to determine whether a normal upstream switch is open or closed. The concept is to send a signal over a line that is modulated, and thereby measure the line impedance. By comparing the impedance of the circuit with the switch closed and with the switch open (during power failure), it is theoretically possible to determine the switch state.